I need to know how to find the polar coordinates of (21, 48); I figured out r (52.4) but I can't figure out the theta even after so many instructional videos! I have the answer (Theta is 66.4) but I can't figure out how to get to it!
+9466 I may not be able to explain any better...but I will try!
Here is just a graph of the point (21, 48).
Theta is the angle that a line from the origin to the point makes with the positive x-axis.
The second one is the same graph, just with some more markings on it.
Look at the second picture. This is just a right triangle! And...in every right triangle,
tan = opposide / adjacent
So..
tan θ = 48/21
θ = atan(48/21)
θ ≈ 66.371º
And we can use the Pythagorean theorem to find the hypotenuse...which is r.
212 + 482 = r2
r = \(\sqrt{441+2304}\approx52.393\) ...just as you found! 
